Method for improving the features of phosphate coating

ABSTRACT

Properties of a phosphate coating are improved by preparing and applying a mixture containing nano-dimensioned hexagonal boron nitride, known as a solid lubricant, to a Zn, Zn-Ca, Fe and Mn phosphate coating. The hexagonal boron nitride is added to the coating bath during the phosphate treatment. Products coated with Zn, Zn-Ca, Fe and Mn phosphate accommodated with hexagonal boron nitride are disclosed.

TECHNICAL FIELD

The present invention is related to the development of a mixture to accommodate nano-dimensioned hexagonal boron nitride in Zn, Zn-Ca, Fe and Mn phosphate coating, to the application of this mixture, and to the products coated with Zn, Zn-Ca, Fe and Mn phosphate accommodated with hexagonal boron nitride.

BACKGROUND ART

Phosphate coating was primarily used for protecting steel against corrosion or for ensuring better adhesion of plastic coating; later on, it started to be used for forming metals or used as lubricant by absorbing oil into its porous structure in order to prevent from friction.

Zn, Zn-Ca and Fe phosphate coating, in general, keeps the oil and forming chemicals used in metal forming processes through extrusion and rolling on the surface. It ensures that forming chemicals bleed as the metal is reformed. The metal will flow easily in these conditions, and the lifetime of the mould will increase since the metal does not stick to the mould.

Mn phospate started to be used to prevent steel corrosion in 1940s. Later on, it became a coating used for lubricating. Due to its hard and porous structure locking the oil inside, it started to be used as the most appropriate coating for corroding environments in need of lubricating. Non-lubricating metal-to-metal contact causes high temperature and high pressure. Such metal-to-metal contact in non-lubricated environments results in corrosion, abrasion, and breakdown of the parts. Here, the importance of preventing metal-to metal friction comes to-the coating stops metal-to-metal contact, and therefore it is commonly used in various sectors such as automotive, refrigerator, air-conditioning compressor, etc. for coating machinery parts, gears, beds and ball-bearings, rings, roller bearings, shafts and similar parts that move one on top of another.

Mn phosphate is a type of phosphate coating bearing the best possible features for abrasion and friction. How to apply Mn phosphate coating is described broadly in patent documents numbered GB 812.095 and GB 1.417.269.

U.S. Patent No. 2004/0062869A1 points out that Mn phosphate coating cannot respond to the recent developments, especially to the need of load for mobile parts and to the longer servicing life, and thus simple manganese phosphate coating cannot be used in certain areas anymore. In order to improve Mn phosphate coating, the coating was covered with surface film using water-based resin containing molybdenum disulfide.

U.S. Pat. No. 1,696,359 discloses application of Mn phosphate for minimizing abrasion in gears and roller bearings, and addition of lubricating phosphor components to the oil for preventing abrasion.

In U.S. Pat. No. 4,662.,67, a Mn phosphate coated compressor part is applied a lubricating film containing molybdenum disulfide, tungsten disulfide, graphite and boron nitride mixed with resin.

In U.S. Pat. No. 6,509,099, Zn phosphate coating used for steel sheets in the automotive sector is applied boron nitride layer, mixed with various types of resin, in order to facilitate forming.

Above-mentioned patents allow for application of a layer containing solid lubricant to improve the features of Mn, Zn, Zn-Ca and Fe phosphate coating. This layer that is added onto the phosphate coating is destroyed after a certain period of time due to abrasion, and the phosphate coating is revealed. Besides, additional procedures are needed for each additional layer, which increases the cost.

With the present invention, a mixture is developed for adding nano-dimensioned particles of hexagonal boron nitride, which is known as a solid lubricant, into the plating bath during the phosphate treatment. As a result of applying this mixture, nano-dimensioned hexagonal boron nitride interlays among the phosphate crystals during formation.

Hexagonal boron nitride improves the lubrication feature of the coated product because hexagonal boron nitride particles have better lubrication properties than the phosphate crystals. Having interlaid among the phosphate crystals, the nano-dimensioned hexagonal boron nitride will endure for a longer period of time compared to the other methods, and no additional process will be required since it is applied during the phosphate coating.

This present invention provides the following benefits:

-   -   1. Preparation of a mixture for adding nano-dimensioned         particles of hexagonal boron nitride to be used in phosphate         treatment into the phosphate coating bath (plating bath) during         the phosphate treatment.     -   2. Addition of nano-dimensioned hexagonal boron nitride into the         bath solution along with this mixture during the phosphate         treatment, which results in its interlaying among the crystals         at the phosphate layer.     -   3. Improving lubrication properties of phosphate coating with         hexagonal boron nitride having a quite low coefficient of         friction (0.15%) and also known as a solid lubricant.     -   4. Saving on time and cost because no additional process is         required since the nano-dimensioned hexagonal boron nitride is         directly added into the phosphate coating bath.     -   5. Endurance by the phosphate layer for a longer period of time         since the nano-dimensioned hexagonal boron nitride interlay         among the phosphate crystals.     -   6. Decrease in the coefficient of friction for the products         coated using this method, and other benefits including         increasing in product life and energy saving in usage due to         less abrasion impact among other benefits that may be guessed by         masters of the subject.

DESCRIPTION OF FIGURES

FIG. 1: Schematic drawing showing nano-dimensioned hexagonal boron nitride particles interlaying among Mn phosphate crystals.

FIG. 2. Zoom (5000x) view of nano-dimensioned hexagonal boron nitride particles among Mn phosphate crystals.

FIG. 3: Zoom (50000x) view of nano-dimensioned hexagonal boron nitride particles among Mn phosphate crystals.

This present invention provides for preparation of a mixture to add hexagonal boron nitride into the Zn, Zn-Ca, Fe and Mn phosphate coating baths. This is a water-based mixture containing hexagonal boron nitride of 0.2 to 10 percent by weight. Hexagonal boron nitride can be used stand-alone; but it is possible to use different additives as well. The mixture also contains, in various ratios, nano-dimensioned solid lubricants (including but not limited to molybdenum disulfide, graphite, tungsten disulfide), surfectants and wetter agents (including but not limited to non-ionic, anionic, cationic, amphoteric surfectants and wetter agents), and phosphate bath chemicals (including but not limited to phosphoric acid solutions containing alkali metal/heavy metal ions, orthophosphoric acid, manganese phosphate salts, oxidants, catalyzers, α-hydroxy acids, EDTA, NTA, DTPA glyconic acids, nickel, tungstate ions). D50 of the hexagonal boron nitride in the mixture is less than 500 nanometer. This mixture containing nano-dimensioned hexagonal boron nitride is well-mixed using mechanical and/or ultrasonic methods prior to addition into the phosphate coating bath. This mixture is added into the phosphate bath at a ratio from 1% to 50% depending on the characteristics of the coating. No other changes are done in terms of coating conditions. When the coating is completed, nano-dimensioned hexagonal boron nitride particles are interlaid among the pores of the phosphate layer formed during the coating process.

FIG. 1 displays a schematic view of nano-dimensioned hexagonal _boron nitride particles interlaying among Mn phosphate crystals. FIGS. 2 and 3, shows the existence of nano-dimensioned hexagonal boron nitride particles, among Mn phosphate crystals, using an electron microscope (SEM). FIG. 2 is a 5000x zoom image that shows Mn phosphate crystals clearly.

The nano-dimensioned hexagonal boron nitride particles among the Mn phosphate crystals are not sharp since they are very small in size. In FIG. 3 however, which is a 50000x zoom image, it is possible to see nano-dimensioned hexagonal boron nitride interlaid between two Mn phosphate as flakes in clear detail.

This present invention decreases the friction coefficient of coating surface with no additional procedure by placing nano-dimensioned hexagonal boron nitride among the Mn, Zn, Zn-Ca and Fe phosphate coating layers. This improvement in the coefficient of friction as well as abrasion resistance due to placement of hexagonal boron nitride particle among Mn phosphate coating makes it possible for various sectors (e.g. automotive, white goods) to use products coated as such. 

1. A method for improving properties of a phosphate coating, the method comprising adding a mixture comprising nano-dimensioned particles of hexagonal boron nitride, known as a solid lubricant, into a phosphate coating bath during a phosphate treatment.
 2. A method for improving properties of a phosphate coating according to claim 1, wherein the to mixture is in at least one of two ways; one being water-based containing only 0.2% to 10% hexagonal boron nitride by weight, and one being water-based containing, in addition to the same amount of hexagonal boron nitride, at least one of a nano-dimensioned solid lubricant, a surfactant and a wetter agent, and a phosphate bath chemical.
 3. A method for improving properties of a phosphate coating according to claim 1, wherein the mixture is added into the phosphate coating bath after being well-mixed using at least one of mechanical and ultrasonic methods.
 4. A method for improving properties of a phosphate coating according to claim 1, wherein the mixture is added into at least of a Zn, Zn-Ca, Fe and Mn phosphate bath at a ratio from 1% to 50% by weight.
 5. A method for improving properties of a phosphate coating according to claim 1, wherein a D50 of the grain size of the nano-dimensioned hexagonal boron nitride added into the phosphate coating is less than 500 nanometers.
 6. A method for improving properties of a phosphate coating according to claim 1, wherein the method improves lubricant properties of the phosphate coating as a result of placement among phosphate crystals during formation.
 7. A method for improving properties of a phosphate coating according to claim 1, wherein the application of the mixture to an Mn phosphate coating will help to decrease the coefficient of friction and increase resistance to abrasion.
 8. A method for improving properties of a phosphate coating according to claim 1, wherein at least one of an applied Zn, Zn-Ca, Fe phosphate coating containing the mixture is used as a preliminary preparation in metal forming so as to decrease the coefficient of friction.
 9. A method for improving properties of a phosphate coating according to claim 1, wherein at least one of an applied Mn, Zn, Zn-Ca, Fe phosphate coating containing the mixture will be help to decrease the coefficient of friction at all surfaces applied.
 10. A method for improving properties of a phosphate coating according to claim 2, wherein the nano-dimensioned solid lubricant comprises at least one of molybdenum disulfide, graphite, and tungsten disulfide.
 11. A method of improving properties of a phosphate coating according to claim 2, wherein the surfactant and wetter agent comprises at least one of a non-ionic, anionic, cationic, and amphoteric surfactant and wetter agent.
 12. A method for improving properties of a phosphate coating according to claim 2, wherein the phosphate bath chemical comprises at least one of a phosphoric acid solution containing alkali metal/heavy metal ions, orthophosphoric acid, a manganese phosphate salt, an oxidant, a catalyzer, an α-hydroxy acid, EDTA, NTA, DTPA glyconic acids, nickel, and tungstate ions.
 13. A method for improving properties of a phosphate coating according to claim 2, wherein the mixture is added into the phosphate coating bath after being well-mixed using at least one of mechanical and ultrasonic methods.
 14. A method for improving properties of a phosphate coating according to claim 13, wherein the mixture is added into at least of a Zn, Zn-Ca, Fe and Mn phosphate bath at a ratio from 1% to 50% by weight.
 15. A method for improving properties of a phosphate coating according to claim 14, wherein a D50 of the grain size of the nano-dimensioned hexagonal boron nitride added into the phosphate coating is less than 500 nanometers.
 16. A method for improving properties of a phosphate coating according to claim 15, wherein the method improves lubricant properties of the phosphate coating as a result of placement among phosphate crystals during formation.
 17. A method for improving properties of a phosphate coating according to claim 16, wherein the application of the mixture to an Mn phosphate coating will help to decrease the coefficient of friction and increase resistance to abrasion.
 18. A method for improving properties of a phosphate coating according to claim 17, wherein at least one of an applied Zn, Zn-Ca, Fe phosphate coating containing the mixture is used as a preliminary preparation in metal forming so as to decrease the coefficient of friction.
 19. A method for improving properties of a phosphate coating according to claim 18, wherein at least one of an applied Mn, Zn, Zn-Ca, Fe phosphate coating containing the mixture will be help to decrease the coefficient of friction at all surfaces applied. 